In connection with so-called jump-lifts, the bottom part of an elevator hoistway is taken into use before the building has been completed. In this case the top part of the elevator hoistway can be constructed at the same time as an elevator moving in the bottom part of the elevator hoistway already serves people on the lower floors of the building. Generally in jump-lifts the elevator car moving in the lower parts of the elevator hoistway is supported and moved during construction-time use with a hoisting machine supported on a platform in the elevator hoistway. The installation work of this machine room platform in the upper parts of the elevator hoistway is done from a movable platform or corresponding in the elevator hoistway, which installation work comprises, among other things, the installation of guide rails and electrification in the elevator hoistway. When the elevator hoistway under construction above the machine room platform has reached a sufficient stage of completion, the completed part of the elevator hoistway can be taken into use. In this case a jump-lift is performed, wherein the machine room platform is raised higher in the elevator hoistway. A worksite crane used in the construction of the building is conventionally used for the jump-lift. One problem with this type of arrangement is that the worksite crane is not always available when needed. This type of solution is presented in, among others, publication GB1194618. Another suggested method for performing the lifting of a machine room platform in connection with a jump-lift is presented in publication EP1583710B1. In the solution in question the vertical support force needed for lifting is taken from the guide rails that are already installed, along which the load is transmitted to the building.
The weight of the machine room platforms combined with the weight of the parts of the elevator supported by the machine room has increased owing to, among other things, buildings that are taller than before. Owing to the very great travel heights of modern elevators, the machine size and rope masses, among other things, are so great that the hoisting capacity needed to perform the last jump-lifts is extremely large. For the same reason, the support needed for the lifting must be robustly made. The aforementioned solution supported on the guide rails cannot, for this reason, be used in all cases, because a weight that is heavier than the machine room platforms cannot be allocated to rest on the guide rails.
Prior-art solutions exist in which a machine room platform that supports the elevator car is lifted with a hoisting device arranged to act between the machine room platform and a support structure that is higher in the elevator hoistway. This can be e.g. a hydraulic hoist such as in publication WO0007923A1. In the solution in question, the hoisting apparatus is large in size, complex, expensive to manufacture and laborious to install.